The fabrication of a bundle of hollow fibers intended to be introduced into a housing for forming a filtration module is a delicate operation by reason of the fragility of these fibers which makes any manipulation difficult. For this reason, several techniques have been set up in order to minimize the number of human interventions during the production of this bundle.
The most commonly used technique is that of knitting a cast mesh on a large weaving frame. The knit obtained is formed by the fibers which form transversely the weft, and by the small chains which support the weft. This sheet is then rolled up into a spiral in such a manner as to form a bundle of parallel fibers. These operations are carried out by means of machines specially conceived for this purpose and only require slight human intervention. However, this techniques has several inconveniences. Firstly, this technique necessitates an initial modification of the machine for the feed of the weft because of the low strength of the fiber, and then for rolling up the sheet into a spiral. Secondly, the filaments of the chain crush the hollow fibers during formation of the small chains. Finally, it is possible that on certain machines the extremity of the fibers forming the bundle is open, which poses problems at the time of production of the filtration module. In effect, the sealing of this module is achieved at each of its extremities, by means of a hardenable resin, termed a potting resin, where risks of penetration of this resin to the interior of the fibers and thus obturating the fibers.
Another technique is described in French Pat. No. 82.07376 and consists in winding the fiber in a crossed manner around a cylinder of a polygonal section. The fibers then are cut at the level of each apex of the cylinder and the sheets thus formed are then rolled into a spiral in such a manner as to form bundles of fibers. This technique leads to the same inconveniences as the previously described technique.
A third technique described in U.S. Pat. No. 4,226,378 consist in rolling up the fiber around a polygonal wheel. The fibers are then cut at the level of each apex of the polygon in such a manner as to directly obtain a number of bundles equal in number to the number of sides of the polygonal wheel. A single machine is thus necessary to achieve the bundle. However, the disadvantage relating to the potting of these bundles in filtration modules remains.
A final technique such as described in French Pat. No. 1,514,200 and Japanese Pat. No. 59.059,217 consists in rolling up the fiber around a support of a polygonal or circular shape, adapted to permit the recovery of the rolled up form. The bundle is then formed by effecting a traction at the point of two diametrically opposed generatrices of this roll. The potting may then be achieved with closed fibers, without risk of penetration of the resin to the interior of these fibers. However, this process also has disadvantages. In the first case, by reason of the sizeable coefficient of friction of these fibers, the fact of carrying out a traction or drawing on the roll usually causes a notable modification of the cross-section of the roll and the arrangement of the fibers. It is thus very difficult to obtain a regular bundle having a predetermined form. Moreover, any traction or drawing, even weak, carried out on the fibers, causes a deformation of the structure thereof by reason of their slight linear elastic zone. For this reason, the hydraulic performances of the fibers is frequently diminished.